A combine harvester usually includes a header attachment that is adapted to cut crop being harvested and that moves the harvested crop into a feeder housing. The feeder housing includes apparatus for lifting the cut crop into threshing and separation areas of the combine. Grain is then separated from stalks of the harvested crop by threshing, beating and possibly also rotary separation apparatus. The grain is then moved to a grain storage or distribution arrangement. Crop residue such as chaff and straw is commonly ultimately deposited onto the ground rearwards of the combine.
Conventional threshing, beating and rotary separation apparatus typically involve feeding the harvested crop between a rotating cylinder and a concave. Such rotating drums and stationary concaves are provided with protrusions or rubbing elements that rub the crop and cause the grain to separate from the ears.
The distance between the concave and the threshing drum is often considered a critical function and may be variable. The distance used may depend on a variety of factors, including for example the size and threshability of the grain. In addition, the concave to drum spacing may be variable to facilitate unplugging.
One problem that may arise involves straw damage and principally the breakage of stalks as threshed straw is passed over from a concave associated with a threshing drum to a concave associated with a beater or a rotary separator. If this occurs to a significant extent, the straw becomes less suitable for some purposes, such as bedding for live-stock. Moreover, short straw makes less neat and stable bales. Furthermore an excess of short straw particles reduces substantially the efficiency of the straw walkers and/or other separation systems. Broken straw may pass down through a gap between the concaves, thereby reducing efficiency of several stages of the cleaning procedure.
In EP-0092599 a device is proposed for varying the distance between a threshing drum of a combine harvester and at least one threshing grate/concave segment pivotally mounted on a threshing concave. The concave segment is moveable and is used to vary the distance between a rear portion of the concave and the threshing drum, this movement being controlled by an adjusting device and acting against a positioning force applied by a spring.
In CA-2130724, a concave for a combine harvester has a rear section that is moveable between a conventional mode position and a folded mode position. In the conventional mode position, the rear moveable section is positioned concentric with the thresher drum and, in the folded mode position, the rear section of the concave extends outwardly from the thresher drum.
In each of EP-0092599 and CA-2130724, a gap exists across the rear edge of the moveable section of concave, at least when in the concentric position. This creates a path by which cracked stalks and other chaff may potentially fall downward and decrease cleaning performance. It also diminishes the separation capacity of a beater drum that is installed behind the threshing drum.